Mirtazapine has a paradoxical effect in which the lower the dose the more sedating it is in general. In other words and according to my doctor and the pharmacist I consulted when I tried it, anything OVER 15 mg becomes less sedating. I tried both 15 mg and 7.5 mg and they both completely left me too fatigued and sleepy the next day. But I have always been sensitive to meds. I was using it for sleep and anxiety. I could not continue with it because I had to be able to function the next day. The pharmacist could not tell me if 22.5 mg would still work for insomnia but not leave me so wiped out the next day and I was too scared to try it. I had read in reviews that a lot of people had tried 3.75 mg (half of a 7.5 mg pill) and it still helped them sleep, but with the paradoxical effect of more sedation at lower doses I was too scared to try it. The first time I ever took it I had only been sleeping 2 hours a night and I slept for 14 hours. No side effects except for being spacey and tired the next day. That was 6 years ago. I tried it one time again last week and the after effects lasted two days this time but I am now 72 years old and even more sensitive to drugs. Only tried it one night this time! Yes (sigh) I have had insomnia for 6 years now with an average sleep of 4 hours a night. Sleep apnea ruled out. I am currently trying Ramelteon and have literally been through all the common sleep meds which either didn’t work or had too many side effects. Ramelteon apparently is not an instant sleep med and can take days or weeks to be fully effective so I will post back with my experience. Luckily no side effects with it and my dosage is 8 mg. Had to find a psychiatrist with more drug side effect knowledge than my GP doc and was blessed to find an amazing lady in Corpus Christi who is so patient and knowledgeable. Insomnia is the most difficult thing I have ever dealt with and my heart goes out to anyone experiencing it. Keep your chin up and remember to take it one day at a time. Also remember that you have made it this far and that the answer may be right around the corner.